1. Field of the Invention
This invention relates to an apparatus for protecting electric power distribution circuits from arc faults. More particularly, it relates to an apparatus which tests the response of an arc fault circuit breaker to an arc generated in the electrical circuit remotely from the circuit breaker.
2. Background Information
Conventionally, circuit breakers have provided protection in electric power distribution circuits against short circuits and current overloads. Recently, there has been rising interest in also protecting such power distribution circuits, and particularly the branch circuits in homes, commercial and light industry applications from arc faults. Typically, miniature circuit breakers are used in such applications. These miniature circuit breakers utilize a thermo-magnetic trip device which incorporates a bimetal responsive to persistent overload conditions and a magnetic armature responsive to the large magnetic forces generated by a short-circuit current. Arc faults are intermittent high impedance faults which can be caused for instance by worn or damaged insulation, and the like. Because of their intermittent and high impedance nature, arc faults do not typically generate currents of sufficient instantaneous magnitude or sufficient average current to trigger the thermo-magnetic trip device which provides the short circuit and overcurrent protection.
Various types of arc fault detectors have been developed and/or proposed. Generally, the detectors are of two types. The first type responds to the random high frequency noise caused by an arc. This high frequency noise tends to be attenuated, especially by the presence of filters on some loads which can be connected to the branch circuit. A second type of arc fault detector looks for the step increases in current each time the arc is struck.
Detection of an arc fault is complicated by the fact that some normal loads can produce waveforms similar to arc faults. Arc fault detectors attempt to distinguish over such phenomena to minimize nuisance faults. The task is further complicated by the fact that, as mentioned above, arc faults tend to be smaller in amplitude than dead faults.
It is known to provide arc fault detectors used in circuit breakers with built-in test circuits for testing their response. However, such an internal test circuit does not guarantee that the circuit breaker will respond to an actual arc fault in a branch circuit remote from the circuit breaker.
There is a need, therefore for apparatus for testing the protection provided to a branch circuit by an arc fault detector including an arc fault detector incorporated in a circuit breaker from actual arc faults occurring in a branch circuit remotely from the detector.